A semiconductor integrated circuit can include a reference voltage pad that can be configured to receive an external reference voltage and supply the external reference voltage to the inside of the semiconductor integrated circuit, an internal reference voltage generator that can be configured to generate an internal reference voltage by voltage dividing, a selector that can be configured to select and output one of the external reference voltage and the internal reference voltage in response to a selection signal, and a voltage trimming block that can be configured to regulate the level of the output voltage from the selector in response to trimming signals and outputs the level-regulated voltage as a reference voltage.